1. Field of the Invention
The present invention relates to an end-of-life estimation device for an air cleaner, for determining a service life of the air cleaner that filters intake air drawn into an internal combustion engine, which is dependent on clogging of the air cleaner.
2. Description of the Related Art
Conventionally, as an estimation device for estimating the end of the service life of an air cleaner, one disclosed e.g. in Japanese Utility Model Registration Publication (Kokoku) No. S58-15895 is known. In this estimation device, attention is paid to the facts that negative pressure on the outlet side of a filter element of an air cleaner disposed in an intake passage is increased due to a loss of pressure of intake air during passing through the filter element, according to the degree of clogging of the filter element and the amount of the intake air, and that a ratio between the negative pressure on the outlet side of the filter element and negative pressure on the inlet side of the filter element becomes approximately constant irrespective of the intake air amount when the degree of clogging of the filter element is equal to a predetermined value.
From this point of view, in the above estimation device, the negative pressure on the outlet side of the filter element is detected by a first pressure converter, and the negative pressure on the inlet side of the filter element is detected by a second pressure converter. Further, an output from the second pressure converter is amplified at a predetermined ratio, and an output from the first pressure converter is compared with the amplified output from the second pressure converter by a comparator. As a consequence, when the output from the first pressure converter is smaller, the degree of clogging of the filter element is not larger than the above-mentioned predetermined value, and hence it is determined that the air cleaner has not reached the end of the service life yet, whereas when the output from the first pressure converter is larger, the degree of clogging of the filter element exceeds the predetermined value, and hence it is determined that the air cleaner has reached the end of the service life.
The above described conventional estimation device basically estimates the degree of clogging of the filter element based on the difference between negative pressure on the upstream side and negative pressure on the downstream side of the filter element, caused by the pressure loss occurring during passing of intake air through the filter element of the air cleaner, and thereby determines the end of the service life of the air cleaner. Therefore, when the intake air amount is small, the pressure loss in the filter element is small, and the difference between the negative pressures on the upstream side and the downstream side of the filter element becomes small, which makes it impossible to always accurately determine the end of the service life of the air cleaner. Further, it is required to dispose the second pressure converter, which is not normally disposed, on the inlet side of the air cleaner as a device dedicated for estimating the end of the service life of the air cleaner. This increases the number of component parts and manufacturing costs of the estimation device.